Tomatoes are revered for their health-boosting properties, but if you slurp your pasta sauce down with a few meatballs, these nutritional benefits appear to undergo an unusual effect.

Many of the purported antioxidant benefits from tomatoes are said to stem from a reddish pigment called lycopene. According to a new study in the journal Molecular Nutrition & Food Research, the levels of lycopene absorbed in a tomato-rich meal significantly dropped if it's accompanied with iron-rich foods, such as meat. 

Scientists at Ohio State University tested the blood and digestive fluid of a very small group of participants (just seven young male students) after they drank a tomato extract shake. Half of the cohort were given a shake laced with an iron supplement, while the others received one without any iron. Their results showed that the participants who had consumed a tomato extract shake with iron had "significantly lower" levels of lycopene in their body compared to those who just drank the tomato shake without the iron supplement.

“When people had iron with their meal, we saw almost a twofold drop in lycopene uptake over time,” lead author Rachel Kopec, an assistant professor of human nutrition at Ohio State, said in a statement.

“This could have potential implications every time a person is consuming something rich in lycopene and iron – say a Bolognese sauce, or an iron-fortified cereal with a side of tomato juice. You’re probably only getting half as much lycopene from this as you would without the iron.”

Lycopene is a carotenoid compound responsible for the red and orange color found in tomatoes,  watermelon, red cabbage, and papayas. Some previous studies have hinted that this pigment holds some antioxidants properties that could help protect people from strokes, heart problems, and perhaps even cancer. There has been considerable interest in its potential role in protecting against prostate cancer. However, many health authorities doubt the extent of these anti-cancer properties.

It’s unclear precisely why iron appears to reduce the uptake of lycopene, as they didn’t look for the underlying mechanism in the study, but the researchers have a few ideas about what’s at play. 

"It’s also possible that iron interrupts the nice emulsified mix of tomato and fats that is critical for cells to absorb the lycopene. It could turn it into a substance like separated salad dressing – oil on top and vinegar on the bottom – that won’t ever mix properly,” said Kopec.